These days, slide switches of the so-called auto return type are widely used in various electronic devices such as portable telephones and digital cameras. The slide switches of this type are operable in two directions for changing a sound volume level or a zooming level, for example, and they return to a neutral position when the operation stops. Such a conventional switch will be described below with reference to FIG. 6 to FIG. 9.
FIG. 6 is a cross-sectional view of a conventional slide switch and FIG. 7 is an exploded perspective view of the same. Case 1 made of an insulating resin in a substantially box shape has a plurality of fixed contacts 2, made of a conducting metal, embedded in its inner side face in the back. On the interior bottom face of case 1, there are disposed rib-like press portions 1A extended from both side faces to oppose each other. Operating member 3 made of an insulating resin has an operating portion 3A forwardly projected from case 1 and a containing portion 3B recessed in the bottom face substantially in the center thereof. In containing portion 3B, there is contained a coiled spring 5 in its slightly pre-compressed state. On both left and right sides of containing portion 3B of operating member 3, there are provided groove portions 3C allowing press portions 1A of case 1 to be inserted therein. Accordingly, operating member 3 is housed in case 1 movably to the left and right. Movable contact piece 4 made of a metal has its center portion fixed to the back side face of operating member 3. Meanwhile, the movable contact piece 4 is slightly bent and has contact points 4A at both ends thereof, and is adapted to make contact with the side face in the back of case 1. Further, cover 6 made of a metal plate is disposed to cover the opening portion at the top of case 1 and thus the slide switch is completed.
Below will be described a method of manufacturing the slide switch as described above.
First, movable contact piece 4 is fixed to operating member 3. Then, while operating member 3 is held with containing portion 3B turned up, spring 5 is compressedly put into containing portion 3B. Then, operating member 3 is turned over and, while operating member 3 is held such that containing portion 3B containing spring 5 faces downward, operating member 3 is put into case 1. Finally by covering the opening portion at the top of case 1 with cover 6, fabrication of the slide switch is completed.
In the above described configuration, when operating portion 3A is moved to the left from the neutral position shown in FIG. 6, the left-hand end of spring 5 gets off the left-hand side face of containing portion 3B with movement of operating member 3 as shown in FIG. 8. At this time, spring 5 is adapted to make contact with press portion 1A on the left-hand side of case 1, and hence, by being pressed thereby against the right-hand side face of containing portion 3B, spring 5 comes to be compressed. Meanwhile, contact points 4A at both ends of movable contact piece 4 fixed to operating member 3 are allowed to resiliently slide along the side face in the back of case 1, whereby the contact points are adapted to make contact with fixed contacts 2 on the left-hand side and in the center. Thus, an electrical connection by the switch is performed via movable contact piece 4. When the operating force on operating portion 3A is released, the right-hand end of spring 5 presses the right-hand side face of containing portion 3B. Then, the biasing force of compressed spring 5 causes operating member 3 to return to its neutral position. When, operating portion 3A is moved in the direction to the right, spring 5 is compressed, oppositely, between press portion 1A on the right-hand side of case 1 and the left-hand side face of containing portion 3B. Hence, contact points 4A of movable contact piece 4 are adapted to make contact with fixed contacts 2 in the center and on the right-hand side.
In the above described conventional slide switch, however, coiled spring 5 generally has ¼ turn of coil-end seating portion 5A at each end thereof as indicated by the hatched portions in FIG. 9. Therefore, the lower half of spring 5 is longer than the upper half corresponding to coil-end seating portions 5A. Accordingly, when spring 5 is compressedly put into containing portion 3B of operating member 3 in assembling work of the switch, coil-end seating portions 5A are adapted to make contact with side faces on the left and right of containing portion 3B and, hence, spring 5 cannot be uniformly compressed. Thus, the center portion of spring 5 bulges upward to cause spring 5 to easily jump off containing portion 3B and come out of position. This makes the assembling work difficult and hence much time is required for assembly.